Clamping mechanism, locking arrangement and method of operating reconfigurable manipulator

ABSTRACT

A clamp mechanism is disclosed, clamping on a tube made of elastic material, provided with a band clamped on a tube. Inside the tube, in the location where the band clamps, a stiff element is located having a diameter substantially corresponding to the inner diameter of the tube. The band encompasses the tube over the length of at least the half of its circumference and is connected to a tensioning and releasing apparatus. A locking system for a manipulator is also provided including tubes substantially parallel to each other. Each tube is formed of curling strip wound on a drum rigidly connected to a structure. The manipulator has at least one reconfigurable parameter. The system includes a mechanism that is mounted on each one of tubes. Further, a method of operating a reconfigurable manipulator is disclosed including curled strip tubes, wherein the manipulator is provided with a locking system, which is released for reconfiguration of the manipulator and clamped for normal operation.

The invention concerns a mechanism clamping on a tube, a system locking a set of tubes and a method of operating a reconfigurable manipulator.

Tubes curled from strips are used in numerous applications in devices characterised by the ability to change their length, which have to combine simultaneously small mass, high durability and high stiffness. This relates in particular to booms, manipulators and antennas used in aviation and space exploration. A tube made of an elastic material, i.e. a material having a high yield strength, e.g. spring steel, after straightening and winding on a drum has small size and mass. Upon unwinding it returns to its nominal form, in which it has been hardened. In this way, after unwinding the strip from the drum a structure forms again constituting a thin-walled tube, characterised by a preferable flexural strength to mass ratio.

An exemplary implementation with the use of curled strips mechanism is a manipulator combining a long reach with a small mass and a small size in folded state disclosed in U.S. Pat. No. 3,601,940. In the folded state the working strip, usually made of metal, is wound onto a rotational drum. After unwinding the strip from the drum there appears a structure resembling a thin-walled tube. Thereby an element is formed with a length adjusted in a significant range by winding and unwinding the strip from the drum. Similar solutions have been disclosed in other documents, e.g. U.S. Pat. No. 3,434,674. In that document preferable ranges of strip thickness have been indicated and the most typical materials for their production have been listed; in particular: carbon steel, stainless steel, beryllium copper, titanium alloys, and fibre composite materials, e.g. glass or polymer, such as Carbon Fibre Reinforced Polymer (CFRP).

A drawback of such structure is that the strip is vulnerable to damage due to loads transferred by the strip region near the drum on which the strip is wound. In applications typical for strips curled into tubes, such as space booms or antennas, transferring large forces and moments is not necessary. However, this technology increasingly expands to other fields, like e.g. servicing manipulators.

The intermediate region II of the strip vulnerable to damage is located between the drum on which the flattened strip is wound and the tube curled from the strip. The strip changes therein its shape from flat to cylindrical—FIG. 1 b. A load applied to the strip in this region can damage it easily. This problem can be solved easily in the case of loads acting in perpendicular to the axis of the curled strip tube. The most typical solution if to use an additional stiffener in the form of a sliding ring or rolls through which passes the strip. However, such solution does not provide protection from loads acting along the tube axis, in particular resulting in the strip buckling. It is difficult to use for compensation of such loads known constructional solutions cooperating with the outer tube surface, such as U-bolts, because thin-walled curled strip tubes are vulnerable to squeezing as well. The solution of these problems is the object of the invention.

This object has been achieved by providing a mechanism clamping on an elastic tube. The clamp mechanism according to the invention, clamps on a partially open tube made of elastic material and locks it with respect to an external structure, with a band. The mechanism according to the invention has a moulder to which the band is attached and tensioning and releasing means for tensioning and releasing the free end of the band. The moulder has a diameter substantially corresponding to the inner diameter of the tube and is adapted to be placed inside the tube, the band is adapted to be led out of the tube through the opening in the tube and encompassing it over a length of at least half of the circumference of the tube and to be tensioned with tensioning and releasing means attached to the structure.

Preferably the tensioning and releasing means are formed by an interface having attached: a tensioning spring and a string connected to a drive so that forces exerted upon the interface by the spring and the string act oppositely along the same direction, wherein the magnitude of the force exerted upon the interface by the string is greater during enforced loosening and smaller during normal operation.

Preferably the number of turns formed by the band on the tube is between one and two.

The object of the invention has been achieved by further providing a system locking a multitubular manipulator. Manipulator has at least two tubes substantially parallel to each other. Each tube being formed of curling strip wound on a drum rigidly connected to a structure. The manipulator has at least one reconfigurable parameter. It further comprises mechanism according to the invention.

Preferably the tensioning and releasing means of each of the mechanisms are attached to the structure.

Preferably the tensioning and releasing means in the mechanisms locking at least two tubes constitute the interfaces having attached to the tensioning springs at one end and couplers at the other, wherein the couplers are connected to a common drive.

Preferably the couplers are strings, and the springs extend radially outside of the system of the tubes so that they are arranged on the straight lines intersecting substantially at one point inside the system of the tubes. At that point there is located a driven axis on which the releasing strings are wound tensioned by the band's springs.

The object of the invention is also achieved by providing a method of operating a reconfigurable manipulator comprising curled strip tubes. The manipulator is provided with a locking system according to the invention, which becomes released for reconfiguration of the manipulator and tightens for normal operation.

Preferably the reconfigurable parameter of the manipulator is its length.

The invention has been described in embodiments illustrated on the drawings, wherein FIG. 1 a shows a drum with a strip curled into a tube known in the art, FIG. 1 b shows the strip's transition from flat shape, enabling winding on the drum, to tubular shape,

FIG. 2 shows the locking mechanism according to the invention,

FIG. 3 a shows an enlarged perspective view of a tube segment and a band of the mechanism according to the invention clamped thereon, omitting the interface between the band and tensioning means, FIG. 3 b shows an enlarged perspective view of a band of the mechanism according to the invention clamped on a tube, with shown interface between the band and the tensioning means, FIG. 4 a shows symbolically a variable length manipulator in the folded state, FIG. 4 b shows symbolically a variable length manipulator in the deployed state, FIG. 5 a shows a front view of a manipulator with a boom composed of three tubes, provided with a system according to the invention, and FIG. 5 b shows a perspective view of a manipulator with a boom composed of three tubes, provided with a system according to the invention.

The locking mechanism according to the invention has been shown in a perspective view in FIG. 2 with the locked open-profile tube 21. An immovable disc to which the mechanism is attached is not shown in the figure. Inside the tube 21 there is a moulder 22 having a diameter corresponding to the inner diameter of the tube 21. A band 23 is attached to the moulder 22 and led out outside the tube through an opening in a partially open tube and wrapped around its circumference, as show in enlargement in FIG. 3 a, where the interface 26 is omitted for a better depiction of the way the strip 23 is wrapped. Tensioning applied to the band's 23 end causes the band to clamp on the moulder 22 and to lock the tube with respect to it. The moulder 22 is made of a stiff material, protecting the tube against crushing and deformation due to clamping the band 23. The band 23 is wound around the tube 21 almost twice. It was verified experimentally that in this situation the band 23 clamps firmly and effectively after tensioning its end, disabling sliding the tube with respect to the moulder 22, while it does not remain clamped after loosening the force tensioning the band's 23 end. The band 23 has a variable width. On the side of the end 231 attached to the moulder 22 it is wider, while on the side of the end 232 it is narrower. The change of the band's width occurs about the half of its length, i.e. at the distance approximately equal to the circumference of the tube 21 from each end 231, 232.

Winding on the tube 21 more than two turns is essentially pointless. It does not result in better adherence of the band nor in a greater contact area, while it causes complications by releasing the locking mechanism. This happens because loosening a greater number of wound turns requires a wider range of movement of the band's end having the tensioning force applied to.

On the other hand, the holding effect can be achieved leading the band along a half of the tube's circumference, but the force suppressing sliding of the tube 21 is then weaker.

To the free end of the band 23 there is attached an interface 26, connected via a spring 25 with the structure 24, what has been shown enlarged in FIG. 3 b. Tension of the spring 25 is chosen such that the band 23 effectively locks the tube 21. To the interface 26 there is connected a string 27 connected to a wheel 29 at a proper distance to its axis, the wheel being driven by a motor 20. The string 27 is directed substantially along the action of the force of the spring 25 such that as the string 27 is wound onto the motor driven wheel 29, a force arises which balances the force of the spring 25 and even slightly greater. Therefore the locking mechanism according to the invention is locked until switching on the motor driving the wheel 29. Instead of the motor, wheel 29 and the string 27 any tensioning or tensioning and releasing means can be used, such as e.g. bi-positional electromagnets or piezoelectric drives. The advantage of their use is the speed of operation.

The mechanism according to the invention can also be preferably applied for thin-walled tubes having a closed profile. Then, the moulder 22 is located inside the tube upon which the band 23 clamps, and is not connected with this band but prevents crushing the tube.

The mechanism according to the invention can be preferably applied to solve the problem of compensating forces acting along the axis of the manipulator comprising curled strips.

The manipulator according to the invention is symbolically shown in FIG. 4 a in the folded state, while in FIG. 4 b in the deployed state. The manipulator comprises a drum 43 with wound thereon a strip 41 curling into a tube after unwinding from the drum. The structure 44 is rigidly attached the drum 43. The locking mechanism 46 according to the invention is attached the structure 44. During winding and deploying the manipulator, the locking mechanism 46 unblocks, allowing transition to the deployed state of the manipulator, shown in FIG. 4 b. However, during operating the manipulator, which can result in longitudinal forces F_(x) applied to the operational end 47 of the manipulator and transferred by the strip curled into the tube 41, the locking mechanism 46 remains locked. Therefore the longitudinal forces F_(x) do not transfer to vulnerable to their action and prone to deformation region II of the strip curled into the tube 41, but are transferred via the locking system 46 to the stiff structure 44. Therefore the longitudinal forces are transferred only via the region III of the strip curled into the tube, where it has cylindrical shape, providing sufficient resistance to their action.

Transferring transversal forces via strips curled into tubes requires an application of more than one tube in a single manipulator. A manipulator with boom comprising three curled strip tubes has proven to be stable and durable. Such manipulator has been shown in cross section view in FIG. 5 a, and in perspective view in FIG. 5 b. Each of these tubes 51 a, 51 b, 51 c curled from strips has to be protected against longitudinal forces. Furthermore, deploying such manipulator is related to the necessity of synchronizing movement of three strips unwound from drums. There strips have to be stopped precisely at the same time. Otherwise, an uncontrolled displacement and/or twisting of the manipulator occur. In such manipulator the locking mechanism according to the invention can be particularly preferably used. This is because the construction of the mechanism according to the invention provides a very easy possibility of synchronizing a number of locking mechanism. On each of the tubes 51 a, 51 b, 51 c the clamping mechanism according to the invention, comprising a band clamping on the tube having the moulder inside, is attached. The end of each band is tensioned by a spring 55 a, 55 b, 55 c. The springs 55 a, 55 b, 55 c extend radially outside of the system of the tubes and are attached to the structure 54 common for all the tubes 51 a, 51 b, 51 c. The straight lines along which the forces of the springs act intersect at one point inside the system of the tubes. In this point there is located a wheel 59 driven by a motor 50. Three strings 57 a, 57 b, 57 c are wound on the axis of the wheel 59. Because of driving the wheel 59 by the motor 50, the strings 57 a, 57 b, 57 c are winding on its axis simultaneously, synchronously loosening the bands clamped on the tubes 51 a, 51 b, 51 c. Thereby all the three mechanisms are released simultaneously.

It is obvious for a person skilled in the art that this principle can be implemented in numerous ways by means of means known in the art. Essential is the configuration of the system where the bands are clamped by default and arranged such that they could be loosened by means of one device located substantially centrally.

The rigid mechanical connection of the structure 54 with the drums having strips wound thereon allows to relieve the intermediate, sensitive region denoted by II in FIG. 1 b, FIG. 4 a, FIG. 4 b. Because the locking mechanisms are connected with the structure 54, the forces acting along the strip in the situation, when the mechanisms are locked, will be transferred to this structure 54 via a rigid connection, and not a drum nor the sensitive region II, wherein the strip changes its shape from flat to circular. Upon releasing the locking mechanisms one retains the possibility to change the length of the curled strip tube by rotating the drum, i.e. the fundamental advantage of the curled strip. A manipulator comprising such system has to be operated in such a way, that normal operations are performed with the locking mechanisms locked on the tubes, while the shape of the manipulator is changed in the conditions of reconfiguration, with the locking mechanisms unlocked. The manipulator must not be then subjected to loads acting along the axes of the strips. In the simplest case, the parameter of the manipulator modified during its reconfiguration can be its length. 

1. A clamp mechanism, clamping on a tube made of elastic material, provided with a band clamping on the tube, characterised in that inside the tube (21), in location where the band (23) clamps there is located a moulder (22) having a diameter substantially corresponding to the inner diameter of the tube (21), wherein the band (23) encompasses the tube (21) over the length of at least half of its circumference and is connected to tensioning and releasing means (25, 27, 29).
 2. A mechanism according to claim 1, characterised in that the tensioning and releasing means (25, 27, 29) are attached to the structure (44, 54).
 3. A mechanism according to claim 1 or 2, characterised in that the tube is partially open and the band (23) has one end (231) attached to the moulder (22) and is led out through the opening in the tube (21), wherein its second end (232) is connected with the tensioning and releasing means (25, 27, 29).
 4. A mechanism according to clam 1 or 2, or 3, characterised in that the moulder (22) is attached to the structure (44, 54), to which the tensioning and releasing means (25, 27, 29) are attached too.
 5. A mechanism according to claim 1 or 2, or 3, or 4, characterised in that the tensioning and releasing means are constituted by an interface (26) attached to the band (23), to which there are connected a tensioning spring (25) and a string (27) connected with a drive so that the forces exerted upon the interface by the spring (25) and a string (27) act oppositely along the same direction, wherein the magnitude of the force exerted upon the interface (26) by the string (27) is greater when the mechanism is not clamped, while smaller when it is clamped.
 6. A mechanism according to any of claims 1 to 5, characterised in that the number of turns formed by the band (23) on the tube (21) is between one and two.
 7. A system locking a multitubular manipulator, characterised in that on each of the tubes (51 a, 51 b, 51 c) there is mounted a mechanism according to any of claims 1 to
 6. 8. A locking system according to claim 7, characterised in that the tensioning and releasing means of each of the locking mechanism are attached to the structure (44, 54).
 9. A system locking a multitubular manipulator according to claim 7 or 8, characterised in that the tensioning and releasing means in the mechanisms locking at least two tubes (51 a, 51 b, 51 c) constitute interfaces having mounted at one end the tensioning springs (55 a, 55 b, 55 c), and couplers at the other, wherein the couplers are connected to a common drive (50).
 10. A locking system according to claim 9, characterised in that the couplers are constituted by strings (57 a, 57 b, 57 c), while the springs (55 a, 55 b, 55 c) extend radially outside of the system of tubes so that they are arranged along straight lines intersecting substantially at one point inside the system of tubes and at that point there is located an axis (58) on which there are wound the strings (57 a, 57 b, 57 c) releasing the bands (53 a, 53 b, 53 c) tensioned by the springs (55 a, 55 b, 55 c).
 11. A method of operating a reconfigurable manipulator comprising curled strip tubes, characterised in that the manipulator is provided with a locking system according to claim 7, which is released for reconfiguration of the manipulator and clamped for normal operation.
 12. A method according to claim 11, characterised in that the parameter of the manipulator subjected to reconfiguration is its length. 